Airspring sleeve

ABSTRACT

An air spring sleeve. The sleeve comprises an elastomer body having two plies. Each ply comprises a cord embedded in the elastomer body. Each cord is wound about the sleeve in an opposing direction from the other and each having a helix angle. The first cord helix angle and the second cord helix angle comprise a cord differential helix angle. The first or inner cord helix angle is greater than a second or outer cord helix angle. The cord differential helix angle is in the range of approximately 0° to 2.5°.

REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from U.S. provisionalapplication serial No. 60/407,361 filed Aug. 30, 2002.

FIELD OF THE INVENTION

[0002] The invention relates to an air spring and more particularly toan air spring sleeve having at least two plies, each ply having a corddifferential helix angle wherein an inner cord helix angle is greaterthan an outer cord helix angle.

BACKGROUND OF THE INVENTION

[0003] Air springs generally comprise a piston and an endcap with anelastomer sleeve connected in an airtight manner between them. Thesleeves may comprise cords embedded in the elastomer body. The cords arewound at a helix angle with respect to a sleeve centerline. The helixangle for each flexible member cord is substantially equal. Equal helixangles contribute to torsional strain and premature failure in airspring sleeves.

[0004] Composite sleeves are also known. They comprise a sleeve having afirst flexible member connected in a partially overlapping manner to asecond flexible member. Each flexible member having a different cordhelix angle. The inner flexible member having a cord helix angle lessthat an outer flexible member cord helix angle with respect to a sleevecenterline.

[0005] Representative of the art is U.S. Pat. No. 5,975,506 (1999) toThurow et al. which discloses an air spring having a composite flexiblemember in which cords are embedded as a reinforcement. The cord angle(a) in the first flexible-member is different from the cord angle β inthe second flexible-member component. Cord angle (a) is less than cordangle β.

[0006] What is needed is an air spring sleeve having little or notorsional strain. What is needed is an air spring sleeve having a cordhelix angle differential wherein the inner cord helix angle is greaterthan an outer cord helix angle. The present invention meets these needs.

SUMMARY OF THE INVENTION

[0007] The primary aspect of the invention is to provide an air springsleeve having little or no torsional strain.

[0008] Another aspect of the invention is to provide an air springsleeve having a cord helix angle differential wherein the inner cordhelix angle is greater than an outer cord helix angle.

[0009] Other aspects of the invention will be pointed out or madeobvious by the following description of the invention and theaccompanying drawings.

[0010] The invention comprises an air spring sleeve. The sleevecomprises an elastomer body having two plies. Each ply comprises a cordembedded in the elastomer body. Each cord is wound about the sleeve inan opposing direction from the other and each having a helix angle. Thefirst cord helix angle and the second cord helix angle comprise a corddifferential helix angle. The first or inner cord helix angle is greaterthan a second or outer cord helix angle. The cord differential helixangle is in the range of approximately 0° to 2.5°.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The accompanying drawings, which are incorporated in and form apart of the specification, illustrate preferred embodiments of thepresent invention, and together with a description, serve to explain theprinciples of the invention.

[0012]FIG. 1 is a cross-sectional view of an air spring.

[0013]FIG. 2 is a detail of a sleeve at A-A in an uninflated state.

[0014]FIG. 3 is a detail of a sleeve at A-A in an inflated state.

[0015]FIG. 4 is a graph depicting torsional strain in air spring sleeveshaving a high cord differential helix angle.

[0016]FIG. 5 is a graph depicting torsional strain in air spring sleeveshaving a preferred cord differential helix angle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017]FIG. 1 is a cross-sectional view of an air spring. Air spring 100generally comprises sleeve 103. Sleeve 103 is connected at each end toendcap 101 and piston 102. Sleeve 103 is constructed of two plies 103 aand 103 b vulcanized together.

[0018] As the air spring is compressed a rolling lobe 104 is formed. Therolling lobe 104 rolls along an outer surface 102 a of piston 102 as thepiston moves relative to the endcap.

[0019]FIG. 2 is a detail at A-A of a sleeve in an uninflated state. Ply103 a is an inner ply disposed inward toward an airspring interior I.Ply 103 b is an outer ply disposed outward of an airspring interior I ascompared to ply 103 a. Each ply 103 a and 103 b comprises a cord 200 and201 respectively, embedded in an elastomer body. The elastomer materialmay comprise a natural or synthetic rubber, or a combination thereof.Cords 200 and 201 comprise aramid having a 1000 denier. Cords 200 and201 may also comprise nylon and polyester, as well as any other textilereinforcements known in the art, and combinations of two or more of theforegoing.

[0020] The technique of building on a mandrel generally comprisesbuilding a preform on a cylindrical mandrel having two plies ofunidirectional cords wound upon an elastomer layer. The cords arespirally wound about the sleeve preform at what is referred to as ahelix angle. The ply cords 200, 201 are wound in opposite wrapdirections. The sleeve is then vulcanized using methods known in theart. More particularly, cords 200 and 201 describe a helix angle θ withrespect to a sleeve centerline CL. Cord 200 is wound first with helixangle θ₁. Cord 201 is wound over cord 200 with a helix angle θ₂ in anopposite direction.

[0021] An important aspect of the quality of a vehicle ride derived fromusing air springs in the suspension is termed harshness. Prior art airsprings have a relatively higher harshness due to a phenomenon whereinat the beginning of the compression stroke the air spring tends tomomentarily rotate about a major axis, axis CL in the instant case seeFIG. 1. More particularly, as the air spring is compressed the airspring will tend to rotate about the compression axis as it attempts tomove axially. This tendency is most pronounced during initialapplication of an impulse by a vehicle suspension to the airspring. Thetendency to initially rotate momentarily impedes the air spring'sability to compress axially. This initial rotation tendency manifests asa momentarily elevated spring rate, which causes an elevated resistanceto axial movement resulting in a momentary inability accommodate asuspension movement or impulse. As such, this tendency contributes tothe harshness of the ride. It has been found that equivalent helixangles in air spring plies cause this behavior, as well as increasedtorsional strain. This behavior leads to premature failure of the airspring sleeve, particularly those having aramid cords. Using plieshaving a helix angle differential as in the instant inventionsignificantly reduces or eliminates such torsional strain, reducesharshness and increases operating life.

[0022] The helix angle controls the inflated diameter and length of theinflated air spring. Prior art sleeves comprise helix angles that areequal, namely, helix angle θ₁ is equal to helix angle θ₂. The helixangle for each ply is generally in the range of approximately 25° to48°.

[0023] In the inventive sleeve, helix angle θ₂ of ply 103 b is less thanhelix angle θ₁ of ply 103 a, resulting in a helix angle differential,Δθ, between the ply cords in the sleeve, namely:

θ₂<θ₁

[0024] This relationship causes a significant reduction or eliminationof a torsional strain in the sleeve, as well as a significant reductionin harshness. The torsional strain reduction is optimized when the helixangle differential is in the range of approximately 2.5° to 0°, namely:

≈2.5°≧Δθ>0°

[0025] The torsional strain reduction is not realized for helix angledifferentials exceeding approximately 5°.

[0026] Further, it has been observed that when the helix angle of ply103 b exceeds the helix angle of ply 103 a, or;

θ₂>θ₁

[0027] a torsional stress in the sleeve is significantly increased,leading to significantly increased harshness and premature failures.

[0028]FIG. 3 is a detail at A-A of a sleeve in an inflated state. As theair spring inflates the helix angle for the first ply and the second plywith respect to an air spring centerline will change, however the helixangle differential as described herein does not significantly change.

[0029]FIG. 4 is a graph depicting torsional strain in air spring sleeveshaving a high cord differential helix angle. Torsional strain is definedas the relative rotational motion of piston 102 as compared to endcap101. More particularly, if during a compression or extension strokepiston 102 partially rotates about an air spring centerline CL withrespect to endcap 101, such relative partial rotation between piston 102and endcap 101 is referred to as torsional strain. For example, zerotorsional strain indicates no relative partial rotation between thepiston 102 and endcap 101.

[0030]FIG. 4 shows a torsional strain for exemplary sleeves A, B, and C.

[0031] The helix angle for each ply in each case is: Helix Angle θ₁ θ₂Δθ A, B, C 40° 45° 5°

[0032] The differential helix angel Δθ for each exemplary sleeve in thegraph is approximately 5°.

[0033] The negative torsional strain values are for a compression strokeand the positive torsional strain values are for an extension stroke.The stroke is approximately 75 mm in each case.

[0034] In examples A, B, and C the helix angle relationship is:

θ₂>θ₁

[0035] In each of these cases the sleeve had significant torsionalstrain, in each case in excess of 1°.

[0036]FIG. 5 is a graph depicting torsional strain in air spring sleeveshaving a preferred cord differential helix angle. Each of the exemplarycases shown in FIG. 5 has a helix angle relationship:

θ₂<θ₁

[0037] The helix angle for each ply in each sleeve is: Helix Angle θ₁ θ₂Δθ A, B, C, D, E, F 41° 39° 2°

[0038] The differential helix angel Δθ for each exemplary sleeve in thegraph is approximately 2°. The negative torsional strain values are fora compression stroke and the positive torsional strain values are for anextension stroke. The stroke is approximately 75 mm in each case.

[0039] One can see in FIG. 5 that the torsional strain for each sleeveis significantly reduced, to approximately 0.15°. This represents asignificant decrease in torsional strain and harshness, therebyincreasing an operational life.

[0040] Although a single form of the invention has been describedherein, it will be obvious to those skilled in the art that variationsmay be made in the construction and relation of parts without departingfrom the spirit and scope of the invention described herein.

I claim:
 1. An air spring sleeve comprising: an elastomer body; a firstcord embedded in the elastomer body, the first cord wound with a firsthelix angle with respect to a sleeve centerline; a second cord embeddedin the elastomer body, the second cord wound with a second helix anglewith respect to a sleeve centerline; the first helix angle and thesecond helix angle describe a differential helix angle; the first cordis disposed inward of an airspring interior; the second cord is disposedoutward of an air spring interior as compared to the first cord; and thefirst helix angle is greater than the second helix angle.
 2. The airspring as in claim 1, wherein the differential helix angle is in therange of approximately 0° to 5°.
 3. The air spring as in claim 2,wherein the differential helix angle is in the range of approximately 0°to 2.5°.
 4. An air spring sleeve comprising: an elastomer body; a firstcord embedded in the elastomer body, the first cord wound with a firsthelix angle with respect to a sleeve centerline; a second cord embeddedin the elastomer body, the second cord wound with a second helix anglewith respect to a sleeve centerline; the first helix angle and thesecond helix angle describe a differential helix angle; the first cordis disposed inward of an airspring interior; the second cord is disposedoutward of an air spring interior as compared to the first cord; and thesleeve having a torsional strain less than 0.5°.
 5. The air spring as inclaim 4, wherein the differential helix angle is in the range ofapproximately 0° to 5°.
 6. The air spring as in claim 5, wherein thedifferential helix angle is in the range of approximately 0° to 2.5°. 7.An air spring sleeve comprising: an elastomer body; a first cordembedded in the elastomer body, the first cord wound with a first helixangle with respect to a sleeve centerline; a second cord embedded in theelastomer body, the second cord wound with a second helix angle withrespect to a sleeve centerline; the first helix angle and the secondhelix angle describe a differential helix angle; and the first helixangle is greater than the second helix angle.
 8. The sleeve as in claim7, wherein: the first cord is disposed inward of an airspring interior;and the second cord is disposed outward of an air spring interior ascompared to the first cord;
 9. The air spring as in claim 8, wherein thedifferential helix angle is in the range of approximately 0° to 5°. 10.The air spring as in claim 9, wherein the differential helix angle is inthe range of approximately 0° to 2.5°.
 11. The air spring as in claim 7,wherein the cord comprises aramid.